PIP technology is often used for subsea pipelines for transporting hydrocarbons. There are many documented benefits of employing PIP pipelines, including good passive insulation. The annulus of a PIP can also include heating elements for further temperature control. Reelable PIP pipeline can be spooled on to a reel and subsequently reeled out by a lay vessel (reel ship). The curvature of the pipeline introduced by the reel has to comply with the bending stiffness of the pipeline, to avoid damage to the pipeline. During laying, the pipeline is passed through a straightener fixed to the ramp at the aft of the lay vessel. The straightener eliminates the curvature of the pipeline introduced by the reel, and/or possibly applies some further bending configuration.
Traditionally, when deploying PIP from a reel, the PIP is cut to an exact length as it comes off the reel, and an end bulkhead is welded to it on the ramp of the lay vessel. This bulkhead is used to connect the pipeline to a connection structure (e.g. a subsea structure). This operation will generally involve cutting, welding, coating and non-destructive evaluation (NDE) of the PIP and bulkhead joint. The operation is relatively slow as it can be difficult to cut and weld the inner and outer pipes of a PIP section, which increases the off-shore time and hence the cost of deployment.
J. Boi et. al., “Development and Application of Reelable PiP Bulkhead Technology,” Offshore Technology Conference (OTC) 23112, describes the use of reelable end bulkheads for lay-down of a fixed length PIP pipeline. The bulkheads can be welded to the PIP, coated and tested on-shore before spooling, which reduces operation time off-shore. However, because the length of the pipeline is fixed, meeting the axial lay tolerances of the pipeline becomes more difficult. This increases the costs for the connection structures and their installation.